With the continuous development of the telecommunication technologies, users' requirements for the access rate of a telecommunication system increase. To meet the requirements for the access rate, more and more importance is attached to Broadband Wireless Access (BWA) telecommunication systems. At present, a telecommunication system that is based on the IEEE 802.16e standard is a typical BWA telecommunication system.
As the radio telecommunication theory illustrates, the higher the transmitting frequency is, the faster the radio wave attenuates with the distance. According to this theory, because the working frequency of the 802.16e telecommunication system is high, the coverage scope of a BS in the system is limited. Accordingly, the IEEE 802.16j workgroup is constructing a radio telecommunication system that is based on the Multi-hop Relay (MR) technology. In an MR telecommunication system, an MS can communicate with a BS through one or more RSs.
In an MR radio telecommunication system, during the handover (HO) of an MS, each potential target BS (among the potential target BSs, one BS may become the target BS that the MS actually hands over to) needs to send the dedicated initial ranging transmission opportunity information to the MS. This information includes the MAC address of the MS (if the serving BS of the MS does not allocate a handover identity, HO_ID, to the MS) or the HO_ID of the MS (if the serving BS of the MS allocates an HO_ID to the MS), and the uplink (UL) transmission opportunity information. The UL transmission opportunity information includes the UL bandwidth, modulation and coding mode, and repeated coding mode. If the MS selects one of the potential target BSs as the HO target BS, the MS uses the dedicated initial ranging transmission opportunity information delivered by the HO target BS to quickly perform ranging, so that the MS can quickly hand over to the target cell.
At present, two methods are available for MS ranging during the HO of an MS.
FIG. 1 is a flowchart of a first method for supporting MS ranging in the prior art. The flowchart includes:
Step 1: The MS sends the MS Handover Request message (MOB_MSHO-REQ) to the serving BS.
Step 2: The current serving BS exchanges information with each neighbor BS or other network entities, such as the Authentication, Service, and Authorization (ASA) server, through the backbone network to determine all the potential target BSs and the public frame (each potential target BS allocates, in a same frame, i.e. the public frame, the dedicated initial ranging transmission opportunity information to the MS).
Step 3: The current serving BS sends the BS Handover Response message (MOB_BSHO-RSP) to the MS. This message carries the ID of each potential target BS, related handover information, and information about the public frame, in which each potential target BS allocates the dedicated initial ranging transmission opportunity information to the MS. The value of this public frame is calculated as follows: ID of the frame when the MS reads the dedicated initial ranging transmission opportunity information—ID of the frame when the MS receives MOB_BSHO-RSP.
Step 4: The MS sends the Handover Indication message (MOB_HO-IND) to the serving BS. The types of this message include “serving BS release”, “HO cancel”, and “HO rejection”. When the type of the message is “serving BS release”, it indicates that the MS determines to hand over.
Step 5: Each potential target BS allocates, in the public frame specified in step 2, the initial ranging transmission opportunity information to the MS. Each potential target BS sets a fast ranging information element (Fast_Ranging_IE) in the UL-MAP of the public frame, so as to allocate the initial ranging transmission opportunity information. If a potential target BS determines to cancel allocating the initial ranging transmission opportunity information to the MS, the BS does not allocate, in the public frame, the initial ranging transmission opportunity information to the MS. That is, during actual processing, the number of potential target BSs that allocate, in the determined public frame, the initial ranging transmission opportunity information to the MS may be 0, 1, or more.
FIG. 2 is a flowchart of a second method for supporting MS ranging in the prior art. Compared with the flowchart of the first method, the flowchart of the second method does not include the process of sending the handover request message from the MS to the current serving BS. In the flowchart of the second method, the current serving BS communicates with neighbor BSs to determine the potential target BSs and the public frame, in which each potential target BS allocates the dedicated initial ranging transmission opportunity information to the MS. The current serving BS carries information about the determined public frame in the BS Handover Request message (MOB_BSHO-REQ) and sends the message to the MS.
The inventor finds at least the following defects of the existing technologies:
In an MR radio telecommunication system, a non-transparent RS has the same ID type with the BS. That is, the MS may treat the non-transparent RS as a BS. In this case, the non-transparent RS may become a potential target BS of the MS. When the MS hands over to the non-transparent RS, fast ranging is required. The existing technology, however, does not provide the method that a non-transparent RS supports the MS's fast ranging.